Hybrid rocket motor having a precombustion chamber

ABSTRACT

A hybrid rocket motor is provided with a precombustion chamber supplied with propellant from separate fuel and oxidizer sources. The propellant can be in the form of gas or liquid and injected substantially tangentially into the head end of the hybrid motor adjacent the oxidizer injector to form a propellant swirl. As the hybrid motor oxidizer is injected into the swirl, it is heated and gasified, and assumes a swirling motion which increases the oxidizer path length and thereby increases the dwell time of the oxidizer. The increased dwell time increases combustion efficiency and permits multiple restarts of the hybrid motor. The propellant may also be a combination of solid and fluid reactants. In one embodiment, the oxidizer injector is extended into the combustion chamber to form a toroidal precombustion chamber which has an annular nozzle adjacent a face of the oxidizer injector.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates broadly to self-propelled projectiles. Moreparticularly, this invention relates to rockets powered by hybridpropellant systems.

2. State of the Art

Rocket boosters (motors) generally fall into three classes: solidpropellant boosters in which a solid fuel element, or grain, undergoescombustion to produce thrust that propels the rocket, liquid propellantboosters that accomplish the same function with a liquid fuel material,and hybrid boosters, described below. Solid and liquid rocket boosterscan produce relatively large amounts of thrust, but for a relativelyshort amount of time. In addition, solid and liquid rocket boosters aregenerally expensive to develop and produce due to the inherent dangersof the highly combustible solid fuels and the complexity of bipropellantliquid feed systems.

Hybrid rocket boosters are described in detail in co-owned U.S. Pat. No.5,715,675 to Smith et al., which is hereby incorporated by referenceherein in its entirety. They have been characterized as a cross betweena solid propellant booster and a liquid propellant booster. Generally,hybrid boosters use a fluid reactant (an oxidizer) to burn a solid fuelelement, although they may use a combustible liquid fuel and a solidreactant. The solid element is generally formed as a thick-walledtubular cylinder, defining a port of a combustion chamber along itslength. The hybrid rocket propellant (fuel and reactant together) can beignited by a pyrotechnic igniter, such as an electrically-generatedspark. The fuel of a hybrid rocket is inert until mixed with theoxidizer in the presence of an igniter in the combustion chamber. Assuch, there is no danger of inadvertent and uncontrollable combustion.

Hybrid rockets are subject to an oscillation in thrust level during burnof the propellant called “combustion instability”. Combustioninstability can vary from severe, oscillating between zero and onehundred percent thrust, to a currently acceptable standard of less thanten percent, and more preferably less than five percent. The inventorshypothesize that the instability is caused by the flame front driftingback and forth along the length of the fuel grain. The drift may becaused by injected oxidizer actually ‘blowing’ out the flame. The resultof flame front drift is a change in the oxidizer/fuel ratio andcombustion efficiency, as well as corresponding thrust levels. Theinstability is most evident in high mass flux ratio (Gt) motors, withthe mass flux ratio calculated as propellant lbs·sec/area of the portmeasured in square inches. In a typical well-designed hybrid motor, anunacceptable level of combustion instability occurs with a mass fluxratio of 0.5 or more. However, a higher mass flux ratio is desired, asincreasing the mass flux ratio permits the diameter of the port withinthe solid fuel to be reduced and the web thickness (thickness of thesolid fuel wall) to be increased, thereby significantly increasing thevolumetric loading of a motor, as well as burn time and total impulse.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a hybrid rocketmotor which burns with high stability.

It is also an object of the invention to provide a hybrid rocket motorhaving a higher mass flux ratio.

It is another object of the invention to provide a hybrid rocket motorwhich increases volumetric loading, burn time, and total impulse.

In accord with these objects, which will be discussed in detail below, arocket is provided which includes a hybrid motor, a casing about thehybrid motor, an aft nose cone, and a rear nozzle. The hybrid motorincludes a storage tank which stores fluid reactant (oxidizer), acombustion chamber, a solid fuel grain defining a central port withinthe combustion chamber, and an injector adapted to inject the oxidizerinto the combustion chamber. According to the invention, a flame holderis provided at a head end of the combustion chamber and maintains aflame adjacent the injector. The flame holder stabilizes the flame frontand prevents the flame front from drifting along the fuel grain, whichthe inventors believe to be a cause of combustion instability, therebyreducing or eliminating combustion instability.

According to one embodiment, the flame holder includes ahigh-temperature casing defining a cavity at the head of the combustionchamber, and a solid propellant within the cavity around or near theinjector. The propellant may be generally cylindrical within acylindrical casing, such that the flame plume of the burning propellantis substantially perpendicular to the oxidizer flow, or may be providedin an annulus within the casing, such that the flame plume from theburning propellant is substantially parallel to the flow of theoxidizer. The solid propellant is preferably ignited substantiallysimultaneously with the ignition of the hybrid motor. The burning of thesolid propellant prevents the flame which results from combustion of thefluid oxidizer and solid fuel in the hybrid motor from drifting, andthereby stabilizes the flame front for the hybrid motor.

According to another embodiment, the flame holder is a precombustionchamber supplied with propellant from separate fuel and oxidizersources. The propellant can be in the form of gas or liquid and injectedsubstantially tangentially into the head end of the hybrid motoradjacent the oxidizer injector to form a propellant swirl. As the hybridmotor oxidizer is injected into the swirl, it is heated and gasified,and assumes a swirling motion which increases the oxidizer path lengthand thereby increases the dwell time of the oxidizer. The increaseddwell time increases combustion efficiency. The precombustion chambercan be held in an “idle” state (i.e., when no hybrid motor oxidizer isinjected through the injector), allowing the hybrid motor to havemultiple restarts without multiple pyrotechnic igniters. Additionally,the precombustion chamber fuel and oxidizer may be adjusted duringhybrid motor burn as needed based on hybrid motor oxidizer flow rates.

According to a further embodiment of the invention, the injector isextended into the combustion chamber to form a toroidal precombustionchamber therebehind which has a controlled exit area (annular nozzle)adjacent a face of the injector. Solid fuel may be provided in thechamber or liquid fuel may be injected therein. In either case, oxidizeris injected into the precombustion chamber, either from a separatesource or from a tap on the main oxidizer line. The oxidizer and fuelmix and travel in a swirling motion and generate heat sufficient tofunction as a flame holder. The heated flow is ejected from the exitarea into the combustion chamber. The precombustion chamber heatgeneration may be controlled or interrupted by control of the flow ofoxidizer into the precombustion chamber.

The additional heat and energy added to the head end of the combustionchamber vaporizes the oxidizer as it is injected into the combustionchamber, thereby maximizing surface area of the oxidizer, and reducingreaction time of the fuel-oxidizer propellants. This operates to ensurethat a flame head does not drift and is stabilized at the injector.

Additional objects and advantages of the invention will become apparentto those skilled in the art upon reference to the detailed descriptiontaken in conjunction with the provided figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a broken schematic longitudinal section view of a rocketprovided with a hybrid motor and a flame holder according to a firstembodiment of the invention;

FIG. 2 is a relatively enlarged broken schematic section view of theflame holder according to the first embodiment of the invention;

FIG. 3 is a broken schematic section view of a flame holder in a rocketbody according to a second embodiment of the invention;

FIG. 4 is a broken schematic longitudinal section view of a rocketprovided with a hybrid motor and a precombustion chamber flame holderaccording to a third embodiment of the invention;

FIG. 5 is a broken schematic section view of the precombustion chamberflame holder according to the third embodiment of the invention;

FIG. 6 is a cross-section across line 6—6 in FIG. 5;

FIG. 7 is a broken schematic longitudinal section view of aprecombustion chamber flame holder in a rocket body according to afourth embodiment of the invention;

FIG. 8 is a relatively enlarged broken schematic section view of thepre-combustion chamber flame holder according to the fourth embodimentof the invention;

FIG. 9 is a cross-section across line 9—9 in FIG. 8; and

FIG. 10 is a broken schematic section view of a precombustion chamberflame holder according to a fifth embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to FIGS. 1 and 2, a rocket 10 includes a hybrid motor 12surrounded by a tubular body 14, a nose cone 16 at a front end of thebody, and an exhaust nozzle 18 at an aft end of the body. The hybridmotor 12 includes a storage tank 20 holding a pressurized fluid oxidizer22, preferably liquid oxygen, and a combustion chamber 24 having a solidfuel 26, such as hydroxyl-terminated polybutadiene (HTPB). The solidfuel 26 defines a central port 28 through the combustion chamber 24. Theoxidizer is fed from the tank 20 through a valved outlet 29 to aninjector 30. A face 32 of the injector includes a plurality of holes 34through which the oxidizer 22 is injected into the combustion chamber24. The oxidizer 22 may be pressurized to the high pressure required forinjection by using a pressurant, e.g., helium or nitrogen, in the tank20, or by using a pump (not shown) between the tank 20 and the injector30.

According to the invention, a flame holder 36 is provided and maintainsa flame adjacent the injector 30. One type of flame holder 36 accordingto the invention includes a casing 38 defining a cavity 40 at the headend of the combustion chamber 24, extending around or adjacent theinjector 30. The casing 38 may be comprised of an injector ring 38 a,and a precombustion ring 38 b, or formed as a unitary construct. Thecasing 38 is made from a material than can withstand high temperaturesand pressures relative to the rocket body 14 material. One preferredmaterial is glass-filled phenolic resin. A solid rocket propellant 42 isprovided within the cavity 40 around or adjacent the injector. Thepropellant 42 is preferably a high metal content propellant such asAP/HTPB (ammonium perchlorate/hydroxyl-terminated polybutadiene), butmay be any other solid propellant known in the art, including, but notlimited to, double base, GAP, gas generator fuels, and black powder.

According to a first embodiment of the invention, the cavity 40 andpropellant 42 are each generally tubular in shape. The solid propellant42 is preferably ignited, e.g., with a pyrotechnic igniter 44,substantially simultaneously with the ignition of the hybrid motor 12.As the web thickness of the solid propellant (the thickness of thepropellant in the direction of its burn) is generally perpendicular to alongitudinal axis A_(L) of the combustion chamber, the burningpropellant 42 creates a flame plume generally in the direction of arrowsP₁; i.e., substantially perpendicular to the flow of oxidizer from theinjector 30. The flame plume functions as a ‘pilot light’ and stabilizesthe flame front at the head end of the combustion chamber and preventsthe flame front from drifting along the fuel grain. The flame holderreduces or eliminates combustion instability caused by flame drift.

The flame holder has a burn time limited by the web thickness. The sizeof the web thickness in the ‘core burning’ configuration of the firstembodiment is limited by the diameter of the combustion chamber, andgenerally smaller than the web thickness of the solid fuel grain. Giventhe relatively limited time over which the flame holder can function,the flame holder of FIGS. 1 and 2 is ideal for short burn, high thrust,liquid oxygen hybrid motors.

Referring to FIG. 3, a hybrid rocket 110 having a second embodiment of aflame holder 136 is shown. The flame holder 136 includes a casing 138about the injector which defines an annular cavity 140 which is providedwith solid propellant 142. The propellant 142 has a web thicknessmeasured substantially parallel to longitudinal axis A_(L) of thecombustion chamber such that it is ‘end burning’ with the flame plumeextending substantially parallel to the flow of the oxidizer; i.e., inthe direction of arrows P₂. In the second embodiment, by adjusting thedepth of the cavity, the web thickness of the solid propellant can beadjusted to correspond to the burn time of a given hybrid system. Infact, unlike the first embodiment, the web thickness of the solidpropellant can be greater than the web thickness of the solid fuelgrain. As such, the second embodiment of the flame holder 136 issuitable for both short and long burn hybrid motors.

Turning now to FIGS. 4, 5 and 6, according to a third embodiment of theinvention, a hybrid rocket motor 212 is provided with a precombustionchamber 250. The precombustion chamber 250 is defined by a casing 238made from a high temperature, high pressure material, such asglass-filled phenolic resin, and provided at the head end of thecombustion chamber 224. The precombusiton chamber 250 is spaced betweenthe oxidizer injector 230 and the solid fuel grain 226. The oxidizerinjector 230 extends into the precombustion chamber 250 such that atoroidal space 251 is defined rearward of the injector face 232.

Coupled to the precombustion chamber 250 are pathways 252, 254 whichterminate at injectors 256, 258 that are oriented to substantiallytangentially direct a gas or fluid into the toroidal space 251 of theprecombusiton chamber 224. A pressurized fuel tank 260 is coupled to oneof the pathways 252, and a pressurized oxidizer tank 262 is coupled tothe other of the pathways 254. Each tank 260, 262 is provided with avalve 264, 266 which controls the flow and flow rate of fuel andoxidizer from the tanks 260, 262, into the pathways 252, 254, throughthe injectors 256, 258 and into the chamber 250. Alternatively, ratherthan using a separate oxidizer tank 262, the oxidizer may be tapped offfrom the main oxidizer tank 222. This option is discussed below withrespect to another embodiment. When the fuel and oxidizer enter theprecombustion chamber, they form a propellant swirl travelling in avortex, as indicated by arrows S, which is combusted to generate heatadjacent the oxidizer injector 230. The fuel and oxidizer may be aself-igniting mixture using: oxidizers such as gaseous or liquid oxygen;pyrophoric materials such as triethyl aluminum, trimethlyl aluminum, ortriethyl borine; and fuels such as propane, ethane or ethylene.Alternatively, the fuel/oxidizer mixture may be hyperogolic(self-igniting oxidizer and fuel), e.g., nitric acid and aniline. Theamount of heat can be adjusted by adjusting the flow rates of the fueland oxidizer into the precombustion chamber.

As the hybrid motor oxidizer from tank 222 is injected into the swirl bythe oxidizer injector 230, it is heated and gasified, and assumes aswirling motion which increases the hybrid motor oxidizer path lengthand thereby increases the dwell time of the hybrid motor oxidizer. Theincreased dwell time increases combustion efficiency. The precombustionchamber can be held in an “idle” state (i.e., when no hybrid motoroxidizer is injected through the injector), allowing the hybrid motor tohave multiple restarts without multiple pyrotechnic igniters.Additionally, the precombustion chamber fuel and oxidizer may beadjusted during hybrid motor burn as needed based on hybrid motoroxidizer flow rates. Moreover, the precombustion chamber 250, includingthe toroidal space 251, defines a recirculation zone in which the flowof heat generated by combustion is recirculated, as indicated by arrowsR, to facilitate holding a flame at the head end of the main combustionchamber 224.

Turning now to FIGS. 7, 8 and 9, according to a fourth embodiment of theinvention, the main oxidizer injector 330 is extended toward thecombustion chamber 324, and a casing 338 is provided against the wall ofthe rocket body 314 and about the main injector 330 to define a toroidalprecombustion chamber 350 about the extension 331 of the main injector.The precombustion chamber 350 has a controlled exit area (annularnozzle) 351 near the face 332 of the injector 330. According to thefourth embodiment, liquid fuel, but not necessarily oxidizer, isinjected into the precombustion chamber via pathways 352 and 354 andthrough two injectors 356, 358 in a manner substantially as described inthe third embodiment; i.e., plumbed from a tank source (not shown) intothe tangential injectors 356, 358. The oxidizer may also be suppliedfrom a separate tank and plumbed into the precombustion chamber as alsodescribed in the third embodiment. Alternatively, as shown in FIG. 8,the oxidizer may be tapped, or may be from the main oxidizer tank 222(FIG. 4) and passed through injector holes 360 in the main injector 330into the precombustion chamber 350. The fuel and oxidizer mix in theprecombustion chamber 350 and travel in a swirling motion imparted bythe tangential injection of the fuel (and possibly oxidizer) and arecombusted. The heated flow of combustion products is ejected from thenozzled exit area 351 into the combustion chamber 324, and functions asa small rocket motor integrally surrounding the main injector 330. Theprecombustion chamber heat generation may be controlled or interruptedby control of the flow of fuel or oxidizer into the precombustionchamber. The additional heat and energy added to the head end of thecombustion chamber vaporizes the oxidizer as it is injected into thecombustion chamber, thereby maximizing surface area of the oxidizer, andreduces reaction time of the fuel-oxidizer propellants. This operates toensure that a flame head does not drift and is stabilized at theinjector.

Turning now to FIG. 10, a fifth embodiment of a precombustion chamber450, substantially similar to the fourth embodiment, is shown. Thecasing 438 defining the chamber 450 also defines a recess 470 which isat least partially filled with solid fuel 472. The oxidizer is suppliedinto the precombustion chamber through tap injectors 460, and combustedwith the solid fuel to provide the same benefit as in the previousembodiment.

By using a flame holder, as described in the several embodiments above,a mass flux ratio in excess 1.0 has been achieved. The increased massflux ratio permits the use of a smaller diameter port (space within thesolid fuel grain), thereby increasing the web thickness of the solidfuel. The result is a significant increase in volumetric loading of thehybrid motor, burn time, and total impulse.

There have been described and illustrated herein several embodiments ofa flame holder and a precombustion chamber for a hybrid rocket motor,and rocket provided with such hybrid motor. While particular embodimentsof the invention have been described, it is not intended that theinvention be limited thereto, as it is intended that the invention be asbroad in scope as the art will allow and that the specification be readlikewise. Thus, while the preferred oxidizer is liquid oxygen, it willbe appreciated that other non-self pressurizing oxidants such as redfuming nitric acid (RFNA), nitrogen tetroxide (NTO), and hydrogenperoxide (H₂O₂), provided with a pressurant such as nitrogen or helium,may also be used, and that self-pressurizing oxidizers such as gaseousoxygen, fluorine, nitrous oxide (NO₂), or carbon dioxide (CO₂) can alsobe used. Furthermore, if H₂O₂ is the oxidant, a fuel component is notrequired in the precombustion chamber. Rather, a catalyst can be usedwith the H₂O₂. The catalyst may be either a solid located in theprecombustion chamber, e.g., samarium nitrate (Sm(NO₃)₃) on silver orsilver-plated nickel mesh, or a fluid injected into the precombustionchamber, e.g., a potassium permanganate solution injectant. Moreover, afuel (either solid or liquid) may then additionally be provided to reactwith the catalyzed H₂O₂.

Also, while the hybrid fuel grain is preferably HTPB, other fuel grainsknown in the art, such as ABS resin, CTPB, PBAN or other fuel/bindersystems may be used.

In addition, while the casing is shown to define particular cavityshapes, it will be appreciated that cavities having other shapes can beused. For example, with respect to the first embodiment of the flameholder (FIG. 2), the casing may be a straight cylinder and define acylindrical cavity provided with cylindrically configured solid rocketpropellant. Also, while in the first and second embodiments webthicknesses have been shown in two exemplar directions, it will beappreciated that the web thickness may be in a direction which isoblique relative to the axis of the combustion chamber. Furthermore, ineach of the first and second embodiments, the solid fuel is spaced fromthe solid propellant such that they are not in contact. This is not arequirement of the invention. Moreover, with respect to theprecombustion chambers, each may be fed oxidizer from the main oxidizertank or from a separate tank. It will therefore be appreciated by thoseskilled in the art that yet other modifications could be made to theprovided invention without deviating from its spirit and scope as soclaimed.

What is claimed is:
 1. A hybrid rocket motor, comprising: a) a containerhaving a first fluid reactant therein and an outlet; b) a maincombustion chamber containing a first solid reactant therein; c) a firstfluid reactant injector between said container and said main combustionchamber through which said first fluid reactant is injected into saidmain combustion chamber to be combusted with said first solid reactant;d) a precombustion chamber at a head end of said main combustionchamber; e) a second fluid reactant which is injected into saidprecombustion chamber; and f) a third reactant which is contacted withsaid second fluid reactant in said precombustion chamber to form acombustible propellant, wherein heat generated from combustion ofcombustible propellant heats said injected first fluid reactant.
 2. Ahybrid rocket motor according to claim 1, wherein: said third reactantis fluid.
 3. A hybrid rocket motor according to claim 2, wherein: saidsecond and third reactants are in a swirl in said precombustion chamber.4. A hybrid rocket motor according to claim 1, wherein: at least one ofsaid second and third reactants is injected substantially tangentiallyinto said precombustion chamber.
 5. A hybrid rocket motor according toclaim 1, wherein: said injector extends along substantially an entiretyof a length of said precombustion chamber, such that an annular nozzlefor said precombustion chamber is defined around said injector.
 6. Ahybrid rocket motor according to claim 5, wherein: said third reactantis solid.
 7. A hybrid rocket motor according to claim 1, wherein: saidfirst and second fluid reactants are the same.
 8. A hybrid rocket motoraccording to claim 7, wherein: said second fluid reactant is plumbedfrom said first container.
 9. A hybrid rocket motor according to claim7, wherein: said second fluid reactant is tapped from holes in saidfirst fluid reactant injector into said precombustion chamber.
 10. Ahybrid rocket motor according to claim 1, wherein: said precombustionchamber is located around or adjacent said first fluid reactantinjector.
 11. A hybrid rocket motor according to claim 10, wherein: saidprecombustion chamber includes a recirculation zone forward of saidfirst fluid reactant injector.
 12. A hybrid rocket motor according toclaim 1, wherein: said first fluid reactant is an oxidizer, and saidfirst solid reactant is a fuel.
 13. A hybrid rocket motor, comprising:a) a container having a first fluid reactant therein and an outlet; b) amain combustion chamber containing a first solid reactant therein; c) afirst fluid reactant injector between said container and said maincombustion chamber through which said first fluid reactant is injectedinto said main combustion chamber to be combusted with said first solidreactant; and d) a precombustion chamber around at least a portion ofsaid first fluid reactant injector, said precombustion chamber having,i) a first inlet for a second fluid reactant, and ii) one of (A) asecond solid reactant and (B) a second inlet for a third fluid reactantwhich when combined with said second fluid reactant forms a combustiblepropellant.
 14. A hybrid rocket motor according to claim 13, wherein:said second fluid reactant is an oxidizer, and said precombustionchamber includes said second solid reactant which is a fuel.
 15. Ahybrid rocket motor according to claim 13, wherein: said second fluidreactant is an oxidizer, and said precombustion chamber includes said atleast one inlet, wherein said third fluid reactant is a fuel.
 16. Ahybrid rocket motor according to claim 15, further comprising: e) asecond fluid reactant tank including said second fluid reactant, saidsecond fluid reactant tank in communication with said first inlet.
 17. Ahybrid rocket motor according to claim 16, further comprising: f) athird fluid reactant tank including said third fluid reactant, saidthird fluid reactant tank in communication with said second inlet.
 18. Ahybrid rocket motor according to claim 16, further comprising: f) saidsecond inlet is in communication with said container, wherein said thirdfluid reactant is said first fluid reactant.
 19. A hybrid rocket motor,comprising: a) a container having a first fluid reactant therein and anoutlet; b) a main combustion chamber containing a solid reactanttherein; c) a main injector between said container and said maincombustion chamber, said main injector having a face with a plurality ofpathways through which said first fluid reactant is injected into saidmain combustion chamber to be combusted with said solid reactant; d) asecond fluid reactant; e) a third fluid reactant stored separately fromsaid second fluid reactant; f) a precombustion chamber at a head end ofsaid main combustion chamber, said second and third reactants beingcombined and combusted in said precombustion chamber to generate heatadjacent said face of said main injector.
 20. A hybrid rocket motoraccording to claim 19, wherein: said first fluid reactant is anoxidizer, and said solid reactant is a fuel.
 21. A hybrid rocket motoraccording to claim 19, wherein: said second fluid reactant is anoxidizer, and said third fluid is a fuel.
 22. A hybrid rocket motoraccording to claim 20, wherein: said first and second fluid reactantsare the same.
 23. A hybrid rocket motor according to claim 22, wherein:said second fluid reactant is stored in said first container.
 24. Ahybrid rocket motor according to claim 19, wherein: said second fluidreactant is selected from the group of gaseous oxygen, liquid oxygen,triethyl aluminum, trimethlyl aluminum, and triethyl borine, and saidthird fluid reactant is selected from the group of propane, ethane andethylene.
 25. A hybrid rocket motor according to claim 19, wherein: amixture of said second and third fluid reactants is hypergolic.
 26. Ahybrid rocket motor according to claim 25, wherein: said second fluidreactant is nitric acid and said third fluid reactant is aniline.
 27. Ahybrid rocket motor according to claim 19, wherein: said main injectorextends substantially through an entirety of a length of saidprecombustion chamber such that an annular exit nozzle for saidprecombustion chamber is defined about said face of said main injector.28. A hybrid rocket motor according to claim 19, wherein: saidprecombustion chamber includes a recirculation zone forward of said faceof said main injector.
 29. A hybrid rocket motor according to claim 19,wherein: said second and third fluid reactants are swirled together. 30.A projectile, comprising: a) a motor having a forward end and an aftend, said motor including, i) a container having a first fluid reactanttherein and an outlet, ii) a main combustion chamber containing a firstsolid reactant therein, iii) a first fluid reactant injector betweensaid container and said main combustion chamber through which said firstfluid reactant is injected into said main combustion chamber to becombusted with said first solid reactant, iv) a precombustion chamber ata head end of said main combustion chamber, v) a second fluid reactantwhich is injected into said precombustion chamber, and vi) a thirdreactant which is contacted with said second fluid reactant in saidprecombustion chamber to form a combustible propellant, wherein heatgenerated from combustion of combustible propellant heats said injectedfirst fluid reactant; b) a tubular body around said motor; c) a noseportion coupled to said forward end of said motor; and d) a nozzlecoupled to said aft end of said motor.
 31. A method of igniting a hybridrocket motor, comprising: a) providing a hybrid rocket motor having aforward end and an aft end, said motor including, i) a container havinga fluid first reactant therein and an outlet, ii) a combustion chambercontaining a solid second reactant combustible with said fluid firstreactant and having a head end and an aft end, iii) an injector betweenthe container and the head end of the combustion chamber; b) providingthird and fourth reactants which when mixed together form a propellant;c) mixing the third and fourth reactants at the head end of thecombustion chamber to form the propellant; d) combusting the propellantsuch that the head end of the combustion chamber is heated; e) injectingthe fluid first reactant through the injector; f) heating the fluidfirst reactant by combustion of the propellant; and g) combusting theheated fluid first reactant with the solid first reactant such that thehybrid rocket motor is ignited.
 32. A method according to claim 31,wherein: the fluid first reactant is an oxidizer and the solid secondreactant is a fuel.
 33. A method according to claim 31, wherein: thesecond and third reactants are fluids.
 34. A method according to claim33, wherein: said mixing includes swirling the second and thirdreactants together.
 35. A method according to claim 31, wherein: thesecond reactant is a fluid and the third reactant is a solid.